Image reading apparatus and light conductor used for the same

ABSTRACT

An image reading apparatus includes a light source for illuminating an image reading region extending in the primary scanning direction, and a plurality of lenses for focusing light reflected on the image reading region and for producing reduced images. Each of the lenses has an optical axis which intersects a predetermined portion of the image reading region. The image reading apparatus further includes a plurality of light receiving elements for output of image signals based on the light focused by the lenses and a light conductor for leading the light emitted by the light source toward the image reading region. The light conductor leads the emitted light so that the predetermined portion of the image reading region is illuminated more brightly than the adjacent portions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image reading apparatus. Moreparticularly, it relates to an image reading apparatus used for making areduced copy of figures, letters, etc drawn on a white board forexample. The present invention also relates to a light conductor usedfor such an image reading apparatus.

2. Description of the Related Art

There are various kinds of image reading apparatuses used for readingimages (figures, letters, etc) printed on a paper sheet or drawn on awhite board. The optical system of such an image reading apparatus mayinclude either selfoc (self-focusing) lenses or convex lenses forfocusing the given original images onto the light receiving elementsincorporated in the reading apparatus. The selfoc lenses, which aredesigned to perform a non-inverting and non-magnifying image-readingfunction, are preferably used for reading out the given images with highresolution. Generally, the selfoc lenses are more expensive than convexlenses. Thus, convex lenses are preferably used when high resolution isnot required.

A conventional image reading apparatus disclosed in JP-A-2(1990)-273257is shown in FIG. 15 of the accompanying drawings. The conventionalapparatus includes a plurality of light receiving elements 91 mounted ona substrate 90, a plurality of convex lenses 92, and a light source (notshown) for illuminating the linear image reading region Sa. When theimage reading region Sa is illuminated by the light source, thereflected light is converged by the convex lenses 92 to focus on thelight receiving elements 91. The images received by the elements 91 arereduced-size, inverted images of the original (see an original arrow Oiand the focused arrow Ri). The light receiving elements 91 output imagesignals whose output levels correspond to the amounts of the receivedlight.

Though conventional image reading apparatuses of the above type arewidely used, they have been found disadvantageous in the followingrespect. As stated above, the conventional apparatus of FIG. 15 usesconvex lenses 92 for its optical system. Thus, even if the image readingregion Sa is uniformly illuminated by the light source, the imagereceived by the light receiving elements 91 may be different in shadefrom the original, thereby failing to be the true image of the original.More specifically, referring to FIGS. 15 and 16, even if the originalarrow Oi (see FIG. 15) is uniformly illuminated by the light source, theshade of the focused image Ri (see FIG. 16) may vary at positions. Thisis because light when passing through the convex lens 92 tends to bedirected closer to the optical axis C of the lens 92. As a result, thecentral portion of D1 of the arrow Ri becomes brighter than its endportions D2, D3 (FIG. 16).

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide an imagereading apparatus which is capable of reproducing the true image of theoriginal even if use is made of size-reducing lenses for the opticalsystem.

Another object of the present invention is to provide a light conductoradvantageously used in such an image reading apparatus.

According to a first aspect of the present invention, an image readingapparatus is provided. The apparatus comprises: a light source arrangedto emit light for illuminating a linear image reading region extendingin a primary scanning direction; a plurality of lenses arranged in anarray for focusing light reflected on the image reading region and forproducing reduced images, each of the lenses having an optical axiswhich intersects a predetermined portion of the image reading region; aplurality of light receiving elements for output of image signals basedon the light focused by the lenses; and a light conductor for leadingthe light emitted by the light source toward the image reading region.The light conductor leads the emitted light so that said predeterminedportion is illuminated more brightly than other portions of the imagereading region which are adjacent to said predetermined portion.

According to a preferred embodiment, the light conductor includes atransparent member having a first surface and a second surface. Thefirst surface faces the light source, while the second surface faces theimage reading region. The transparent member is arranged to lead lightfrom the first surface to the second surface so that distribution oflight at the first surface is different from distribution of light atthe second surface.

Preferably, the transparent member may be formed with a plurality ofindents facing the image reading region. Each of the indents may beprovided with an inclined portion slanted relative to the first surfaceof the transparent member.

According to a preferred embodiment, the transparent member may beformed with a plurality of projections facing the image reading region.Each of the projections may have a corner at which a cutout is provided.

The light source may include a plurality of light-emitting diodesarranged in an array. The light-emitting diodes may be offset in theprimary scanning direction from the optical axes of the respectivelenses.

Preferably, each of the light-emitting diodes may be held in facingrelation to a relevant one of the inclined portions of the indents.

The image reading apparatus may further comprise a casing for supportingthe light source, the lenses, the light receiving elements and the lightconductor. The light conductor may protrude partially from the casingtoward the image reading region.

According to a preferred embodiment, the first surface of thetransparent member may be formed with a convex portion facing the lightsource.

According to another preferred embodiment, the light conductor mayinclude a first transparent member and a second transparent member.Further, the light conductor may include more than two transparentmembers.

Preferably, the first transparent member may be provided with a lightreceiving surface facing the light source and a light emitting surfaceopposite to the light receiving surface. At least either one of thelight receiving surface and the light emitting surface may be providedwith a convex portion extending in the primary scanning direction.

According to a preferred embodiment, the second transparent member maybe formed separately from the first transparent member. The secondtransparent member may be arranged to lead light emitted from the lightemitting surface toward the image reading region.

Preferably, both the light receiving surface and the light emittingsurface of the first transparent member may be convex.

Preferably, the second transparent member may be provided with a lightreceiving surface held in facing relation to the light emitting surfaceof the first transparent member.

According to a preferred embodiment, the light receiving surface of thesecond transparent member may be sinuous.

The image reading apparatus may further comprise light shielding membersarranged between the light emitting surface of the first transparentmember and the light receiving surface of the second transparent member.

Preferably, the first and the second transparent members may be fixed toeach other. To this end, the first transparent member may be formed witha positioning groove, while the second transparent member may be formedwith a leg portion fitted into the positioning groove of the firsttransparent member.

According to a second aspect of the present invention, there is provideda light conductor which comprises: a first surface for receiving light;a second surface for allowing the light to exit; and a plurality ofindents defined by the second surface. Each indent is provided with aninclined portion slanted relative to the first surface.

According to a third aspect of the present invention, there is provideda light conductor which comprises: a first transparent member providedwith a first light receiving surface and a first light emitting surfaceopposite the first light receiving surface, at least either one of thefirst light receiving surface and the first light emitting surface beingformed with a convex portion; and a second transparent member formedseparately from the first transparent member and provided with a secondlight receiving surface held in facing relation to the first lightemitting surface of the first transparent member, the second transparentmember being also provided with a second light emitting surface forallowing light to exit.

Other features and advantages of the present invention will becomeapparent from the detailed description given below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the principal parts of an imagereading apparatus according to a first embodiment of the presentinvention;

FIG. 2A is a sectional view taken along lines X1—X1 in FIG. 1;

FIG. 2B is a sectional view taken along lines X2—X2 in FIG. 1;

FIG. 3A is a plan view showing a light conductor used for the imagereading apparatus of FIG. 1;

FIG. 3B is a front view showing the light conductor of FIG. 3A;

FIG. 3C is a side view showing the same light conductor;

FIG. 4 is an enlarged view showing a principal portion of the same lightconductor;

FIG. 5A is a sectional view showing a principal portion of a modifiedlight conductor;

FIG. 5B is a sectional view showing a principal portion of a lightconductor compared to the modified light conductor of FIG. 5A;

FIG. 6 is a sectional view showing a principal portion of anothermodified light conductor;

FIG. 7 is a sectional view showing a principal portion of still anothermodified light conductor;

FIG. 8 is a sectional view showing an image reading apparatus Rbaccording to a second embodiment of the present invention;

FIG. 9 is a sectional view taken along lines X3—X3 in FIG. 8;

FIG. 10 is a sectional view taken along lines X4—X4 in FIG. 8;

FIG. 11 is a perspective view showing a first transparent member usedfor the image reading apparatus of the second embodiment;

FIG. 12A is a front view showing a second transparent member used forthe image reading apparatus of the second embodiment;

FIG. 12B is a side view showing the second transparent member of FIG.12A;

FIG. 13 is a sectional view showing a principal portion of a modifiedfirst transparent member;

FIG. 14 is a sectional view showing a modified light conductingassembly;

FIG. 15 is a sectional view showing a principal portion of aconventional image reading apparatus; and

FIG. 16 is a diagram for illustrating the function of a convex lens usedfor the conventional apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be describedbelow with reference to the accompanying drawings.

Reference is first made to FIGS. 1-4 illustrating an image readingapparatus Ra according to a first embodiment of the present invention.The image reading apparatus Ra is described as applicable for readingout images (figures, letters, etc) written on a white board WB, thoughthe present invention is not limited to this example.

In FIG. 1, the white board WB is depicted as extending horizontally, andthe image reading apparatus Ra is disposed below it. This composition isadopted merely for convenience of illustration. Actually, the whiteboard WB is held in an upright position, so that the writing surface ofthe board WB is readily accessed.

As seen from FIG. 1 or 2B, the image reading apparatus Ra includes acasing 1, a convex lens array 2, a lens array cover 3, a light conductor4, a light source 5, a plurality of light detectors 6 and an insulatingsubstrate 7. As will be described in detail hereinbelow, the lightconductor 4 serves to adjust or alter the distribution of light emittedfrom the light source 5. As shown in FIG. 2B, each light detector 6 isprovided with a predetermined number of light receiving elements 60.

The casing 1, which may be made of a synthetic resin material, has anelongated configuration, as seen from FIGS. 2A and 2B. The casing 1 isprovided with first and second hollow portions 10 and 11 both of whichare open upward and downward (as viewed in FIG. 1). The first and thesecond hollow portions 10, 11 are elongated longitudinally of the casing1. As will be described below, components required for the readingapparatus Ra are accommodated in either the first hollow portion 10 orthe second hollow portion 11. The casing 1 is carried by a movablesupporting member (not shown) in facing relation to the white board WB.The casing 1 is caused to move in a secondary scanning direction N2(FIG. 1) by the non-illustrated supporting member. The distance betweenthe casing 1 and the white board WB is kept constant as the casing 1 ismoved in the secondary scanning direction N2.

As shown in FIG. 2B, the lens array 2 includes a plurality of convexlenses 20 held together by a holder 21 made of e.g. a synthetic resinmaterial. As shown in FIGS. 1 and 2B, the lens array 2 is fitted intothe first hollow portion 10 and positioned at a suitable height in thefirst hollow portion 10. The convex lenses 20 are arranged at regularintervals in a primary scanning direction N1 (FIG. 2A) perpendicular tothe secondary scanning direction N2 (FIG. 1).

In the illustrated embodiment, the holder 21 is prepared separately fromthe respective convex lenses 20.

Alternatively, the holder 21 and the convex lenses 20 may be integrallymade of a synthetic resin material. A linear image reading region S onthe white board WB extends in the primary scanning direction N1 (seeFIG. 2B). As shown in FIG. 1, the image reading region S is intersectedby the optical axes C of the respective convex lenses 20.

As shown in FIG. 1, the lens array cover 3, which may be made of adark-colored (e.g. black) synthetic resin material, is fitted into thefirst hollow portion 10 to come into direct contact with the upperportion of the lens array 2. The lens array cover 3 ensures properpositioning of the lens array 2. The lens array cover 3 is formed with aplurality of through-holes 30 corresponding in number and position tothe convex lenses 20, as seen from FIG. 2B. Each through-hole 30 servesas a light-restricting aperture for adjusting the amount of lightincident on a relevant one of the convex lenses 20. The center of eachthrough-hole 30 coincides with the optical axis C of the relevant convexlens 20.

In the illustrated embodiment, as seen from FIG. 1, the inner diameterd1 of each through-hole 30 is smaller than the diameter d2 of therelevant convex lens 20. In this manner, light is prevented fromentering each convex lens 20 at its radially outer portion (i.e.,peripheral portion). Thus, the focusing of light is performed only bythe central portion of each convex lens 20, which is advantageous forgenerating a clearly focused image. If the diameter d₁ of eachthrough-hole 30 is much greater, the focused image will be brighter.Unfavorably, however, the distinctness or sharpness of the image may becompromised.

The light detectors 6 are mounted on the obverse surface of thesubstrate 7. As shown in FIG. 2B, the light detectors 6 are arranged atregular intervals in the primary scanning direction N1. Thus, the lightreceiving elements 60 of the respective light detectors 6 are arrangedin a row extending in the primary scanning direction N1. The lightreceiving elements 60 convert received light into an electric signalbased on the amount of the received light. The substrate 7 is attachedto the bottom portion of the casing 1 to close the downward openings ofthe first and the second hollow portions 10, 11. As shown in FIGS. 1 and2B, each light detector 6 is held in facing relation to a relevant oneof the convex lenses 20 when the substrate 7 is fixed to the casing 1.With such an arrangement, images illuminated at the image reading regionS are focused onto the light detectors 6 through the convex lenses 20,as shown in FIG. 2B.

Referring to FIGS. 1 and 2A, the light source 5 includes a plurality oflight emitting devices 50 such as light-emitting diodes (LEDs). Thelight emitting devices 50, which are mounted on the obverse surface ofthe substrate 7, are received in the second hollow portion 11 when thesubstrate 7 is attached to the casing 1. As shown in FIG. 2A, the lightemitting devices 50 are spaced from each other in the primary scanningdirection N1. As illustrated, two light emitting devices are arrangedadjacent to a corresponding one of the optical axes C of the respectiveconvex lenses 20.

Specifically, the light emitting devices 50 a, 50 b (which come firstand second from the left in FIG. 2A) are arranged close to the firstoptical axis C₁, the next two light emitting devices 50 c, 50 d close tothe second optical axis C₂, and so on. The first paired light emittingdevices 50 a, 50 b are arranged symmetrically with respect to the firstoptical axis C₁, the second paired light emitting devices 50 c, 50 dwith respect to the second optical axis C₂, and so on. In theillustrated embodiment, any paired light emitting devices 50 are spacedfrom the relevant one of the optical axes C by a predetermined distanceL (see the fourth optical axis C₄ and the paired light emitting devices50 g, 50 h).

Preferably, each light emitting device 50 may include a combination oftwo LEDs of different colors. One of these two LEDs may be designed toemit green light, while the other may be designed to emit red light.With such an arrangement, when only the red LEDs are turned on to emitred light, red portions of the images at the image reading region S arenot read out by the light detectors 6. On the other hand, when the greenLEDs are turned on, all the images at the image reading region S may beread out by the light detectors 6. Thus, by comparing the read-outimages obtained at one time (when only the red LEDs are turned on) withthe other read-out images obtained at another time (when only the greenLEDs are turned on), it is possible to distinguish the red portions fromthe other portions of the images at the image reading region S. In thismanner, a two-color image-reading function can be performed. Thisfunction is particularly advantageous in making a copy of images writtenon the white board WB since these images are often written in black orred. It should be noted, however, that the present invention is notlimited to this example. For instance, the light source may be designedto emit white light or light of a single color such as green.

According to the present invention, a single, linear cold cathode tubemay be used for the light source 5 in place of the light emittingdevices 50.

The light conductor 4 includes a transparent member 40. Preferably, thetransparent member 40 may be made of a material having high transparencyand high mechanical strength. The examples of such a material may bepoly(methyl methacrylate) (PMMA) or polycarbonate (PC). In theillustrated embodiment, the light conductor 4 is constituted by a singletransparent member. However, as will be described later, the lightconductor 4 may be made up of more than one transparent member.

As shown in FIGS. 3A and 3B, the transparent member 40 has an elongated,generally plate-like configuration. Referring also to FIG. 3C, thetransparent member 40 is provided with a first side surface 40A, asecond side surface 40B, a third side surface 40C and a fourth sidesurface 40D. The first side surface 40A is opposite to the second sidesurface 40B, while the third side surface 40C is opposite to the fourthside surface 40D. As best shown in FIG. 3B, the transparent member 40has two ends 40E which are spaced from each other in the longitudinaldirection of the transparent member 40. Each end 40E is formed with aprotrusion 41 for properly positioning the transparent member 40relative to the casing 1 (see FIG. 2A). In place of the protrusions 41,the transparent member 40′ may be formed with two retreated portions atthe respective ends 40E.

Preferably, each of the above-mentioned side surfaces 40A-40D may be asmooth surface. Advantageously, each side surface may be an extremelysmooth surface or mirror surface. When the first to the fourth sidesurfaces 40A-40D are sufficiently smooth, light propagating through thetransparent member 40 can be totally internally reflected on thesesurfaces when it meets them at an incidence angle greater than thecritical angle. As is known, the critical angle depends on the materialmaking the transparent member 40. When light propagating through thetransparent member 40 meets the side surfaces 40A-40D at an incidenceangle smaller than the critical angle, it goes out of the transparentmember 40 through these side surfaces.

As shown in FIGS. 1 and 2, the first side surface 40A is held in facingrelation to the light emitting devices 50. Thus, when the light emittingdevices 50 are turned on, light emitted from them enters the transparentmember 40 at the first side surface 40A.

Referring to FIG. 4, the first side surface 40A of the transparentmember 40 is provided with a central convex portion 40 a and twoconcaved portions 40 b flanking the convex portion 40 a. The convexportion 40 a and the concaved portions 40 b extend longitudinally of thetransparent member 40 and have an unvarying cross section over theentire length of the first side surface 40A. As illustrated, the crosssection of the convex portion 40 a is so configured as to cause theradially emitted light beams from the light emitting devices 50 totravel generally in parallel to the optical axis C₇ of the convexportion 40 a. Preferably, the concaved portions 40 b may have agenerally arcing contour whose center of curvature coincides with theposition P from which light of the light emitting devices 50 originates.With such an arrangement, the incidence angle of light meeting theseconcaved portions 40 b can be substantially zero. Thus, the totalreflection of the light upon meeting the concaved portions 40 b does notoccur, whereby the light will efficiently propagate into the transparentmember 40.

Referring back to FIGS. 3A-3C, the second side surface 40B serves as alight emitting surface from which the light propagating through thetransparent member 40 is let out. As best shown in FIG. 3B, the secondside surface 40B is provided with a plurality of generally V-shapedindents 42 arranged at regular intervals in the longitudinal directionof the transparent member 40. Each V-shaped indent 42 is defined by apair of inclined portions 42 a and a bottom portion 42 b of the secondside surface 40B. The lower ends of the respective inclined portions 42a are connected to each other by the bottom portion 42 b. The distancebetween the lower ends of the respective inclined portions 42 a issmaller than the distance between the upper ends of the same inclinedportions 42 a. In addition to the inclined portions 42 a and the bottomportions 42 b, the second side surface 40B is formed with level portions43 extending generally in parallel to the first side surface 40A. Theselevel portions 43 together with the inclined portions 42 a define aplurality of truncated projections 45.

The third side surface 40C and the fourth side surface 40D are arrangedto totally reflect the light propagating through the transparent member40 for enabling the light to be efficiently led from the first sidesurface 40A to the second side surface 40B. As shown in FIG. 3C, thetransparent member 40 as a whole is not upright but bent. Thus, as shownin FIG. 1, the first side surface 40A of the transparent member 40 isheld in facing relation to the light emitting devices 50 (arranged awayfrom the optical axes C), while the second side surface 40B is directedto the image reading region S (intersecting the optical axes C).

As shown in FIG. 1, the lower portion of the light conductor 4 (i.e.,the portion containing the first side surface 40A) is received in thesecond hollow portion 11 of the casing 1 in a manner such that the firstside surface 40A extends in the primary scanning direction. On the otherhand, the upper portion of the light conductor 4 (i.e., the remainingportion containing the second side surface 40B) protrudes from thecasing 1 toward the image reading region S.

As shown in FIG. 2A, the light conductor 4 is,fixed to the casing 1 in amanner such that the center of the bottom portion 42 b of each V-shapedindent 42 intersects a corresponding one of the optical axes C. Thus,each V-shaped indent 42 is halved by the relevant optical axis C. Asillustrated, each of the light emitting devices 50 is positioned below acorresponding one of the inclined portions 42 a of the transparentmember 40.

The function of the image reading apparatus Ra having theabove-described arrangements will now be described.

Referring to FIG. 1, when the light emitting devices 50 are turned on,the light emitted from them enters the transparent member 40 through thefirst side surface 40A. Then, the light will propagate through thetransparent member 40 to reach the second side surface 40B. During thetravel from the first side surface 40A to the second side surface 40B,the propagating light may strike the third side surface 40C and/or thefourth side surface 40D to be totally reflected, or it may directlyreach the second side surface 40B from the first side surface 40Awithout meeting the third or fourth side surface.

As stated above, light beams passing through the convex portion 40 a ofthe first side surface 40A are directed in the, same direction, so thatthey will propagate in parallel to the optical axis C₇. Advantageously,the parallel light beams are effectively led to the second side surface40B. Further, as shown in FIG. 1, the convex portion 40 a is arrangedabove the light emitting devices 50. Thus, most of the light emittedfrom the light emitting devices 50 will strike the convex portion 40 a,and therefore be efficiently led to the second side surface 40B. Even ifthe emitted light misses the convex portion 40A, it may meet either oneof the two concaved portions 40 b arranged adjacent to the convexportion 40 a. Thus, the light emitted from the light emitting devices 50is properly led through the transparent member 40 from the first sidesurface 40A to the second side surface 40B, thereby minimizing loss oflight.

As shown in FIG. 2A, when light strikes the inclined portions 42 a ofthe second side surface 40B, it may be totally inwardly reflected bythem. The critical angle for total inward reflection may be 45 degreesfor example. The possibility of such total inward reflection is greaterespecially when light emitted from one of the light emitting devices 50directly reaches the inclined portion 42 a which is located right abovethe particular one of the light emitting devices (for example, see thefifth light emitting device 50 e and the light emitted therefrom). Thetechnical advantage obtained from this arrangement is as follows.

If use is not made of the light conductor 4, the light emitting devices50 illuminate more brightly the particular portions of the region Slocated right above the respective light emitting devices 50 than theother portions of the region S. In the image reading apparatus Ra, onthe other hand, the propagating light tends to be totally inwardlyreflected on the inclined portions 42 a of the second side surface 40B.Thus, the illumination pattern at the image reading region S with thelight conductor 4 provided is different (i.e., altered) from theillumination pattern with no light conductor provided.

As shown in FIG. 2A, when the light propagating through the transparentmember 40 meets the bottom portions 42 b of the second side surface 40B,it may pass through them without being reflected (see an arrow Naextending from the fifth light emitting device 50 e). As viewed in theprimary scanning direction N1, the bottom portions 42 b overlap theoptical axes C of the convex lenses 20. On the other hand, the lightemitting devices 50 are offset from the optical axes C by the distanceL. Thus, as shown by the above-mentioned arrow Na, the light emittedfrom a light emitting device 50 will travel away from the optical axis Cafter passing through the bottom portion 42 b. This means that the lightexiting the transparent member 40 via the bottom portions 42 b may notilluminate the portions of the image reading region S which intersectthe optical axes C.

In the image reading apparatus Ra, as seen from the above, the opticalaxis-intersecting portions of the image reading region S are illuminatedless brightly than when no light conductor is provided. In theillustrated embodiment, each bottom portion 42 b is rendered flat, sothat light is allowed to pass through without being reflected.Alternatively, the bottom portion 42 b may be curved so as to causelight to be totally inwardly reflected more frequently.

When the light propagating through the transparent member 40 meets thelevel portions 43 of the second side surface 40B, the light tends topass through them since the incidence angle is often smaller than thecritical angle for total inward reflection. As shown in FIG. 2A, eachlevel portion 43 is located between the two adjacent optical axes C tobe spaced therefrom. Thus, the light exiting the transparent member 40via the level portion 43 illuminates only a limited portion of the imagereading region S which is located between the two adjacent optical axesC.

Since the light conductor 4 is designed as described above, it ispossible to illuminate more brightly the portions of the image readingregion S which are spaced away from the optical axes C than theremaining portions which are closer to the optical axes C. According tothe present invention, the design of the illustrated light conductor 4may be modified so that the illumination at the image reading region Swill have a different pattern. For instance, the inclination and lengthof the respective inclined portions 42 a may be made greater or smaller.By adjusting the configuration of the light conductor 4, it it possibleto realize a desired illumination pattern at the image reading region S.For instance, it is possible to gradually change the brightness of theillumination pattern in accordance with the distance from the opticalaxes C.

Referring now to FIG. 2B, when the image reading region S isilluminated, the reflected light is focused onto the light detectors 6by the convex lenses 20. The focused image is inverted and reduced insize as compared to the original image. Based on the received light, thelight receiving elements 60 of the light detectors 6 will output imagesignals. Each of the illustrated lenses 20 is an ordinary convex lens.Thus, when an original image is illustrated with uniform brightness, theresulting image focused by the convex lens 20 will be brighter in aportion adjacent to the optical axis of the lens than in the otherportions. However, in the image reading apparatus Ra of the presentinvention, the optical axis-intersecting portions of the image readingregion S are illuminated less brightly than the other portions. Sincethe effect of this nonuniform illumination is cancelled out by theabove-described light-focusing behavior of the convex lenses 20, theimage focused onto the light detectors 6 reflects the true shades of theoriginal image.

FIG. 5A shows a modified light conductor 4A usable for the image readingapparatus Ra. The light conductor 4A is provided with V-shaped concavedportions 42 and truncated projections 45 similar to those of the lightconductor 4 (see FIG. 2A). Each truncated projection 45 of the modifiedconductor 4A, however, is formed with two cutouts 46 disposed at itscorners. Such an arrangement is advantageous in preventing concentrationof light emission which might otherwise occur at the corners.Specifically, if such cutouts are not provided and the respectivetruncated projections 45 have two round corners R, as shown in FIG. 5B,light tends to be concentrated at these round corners R. As a result, anunduly large amount of light may be emitted from the round corners Rtoward the image reading region. This problem may be readily overcome orat least reduced by forming cutouts 46 at the corners of each truncatedprojection 45.

FIG. 6 shows another modified light conductor 4B. The transparent member40 has a sinuous second side surface 40B. As illustrated, the secondside surface 40B defines a plurality of convex portions 42A and shallowconcaved portions 42 arranged alternately with the convex portions 42A.It is clear that the light conductor 4B functions in the same manner asthe light conductor 4 of FIG. 2A.

FIG. 7 shows another modified light conductor 4C. The transparent member40 of the light conductor 4C is provided with a flat first surface 40Aand a flat second surface 40B extending in parallel to the first surface40A. As illustrated, a plurality of light shielding pieces 44 are fixedto the second surface 40B. These shielding pieces 44 are arranged atregular intervals in a row extending longitudinally of the transparentmember 40. Each light shielding piece 44 is opaque or less transparentthan the transparent member 40. Each light shielding piece 44 may haveuniform transparency (or opaqueness). Alternatively, the transparency ofeach light shielding piece 44 may be varied in accordance withpositions. For instance, the opaqueness of the illustrated lightshielding piece 44 a may be gradually increased from the left side 44Lto the right side 44R.

Reference is now made to FIGS. 8-12B illustrating an image readingapparatus Rb according to a second embodiment of the present invention.

As shown in FIG. 8, the image reading apparatus Rb includes a casing 1′,a lens array 2′, a lens array cover 3′, a light conducting unit U′, alight source 8′, a plurality of light detectors 6′, and an insulatingsubstrate 7′. The light conducting unit U′ is made up of a firsttransparent member 4′ and a second transparent member 5′.

The casing 1′, which may be made of a synthetic resin material, has anelongated configuration. The casing 1′ is provided with first and secondhollow portions 10′ and 11′ both of which are open upward and downward.The first and the second hollow portions 10′, 11′ are elongatedlongitudinally of the casing 1′. As will be described below, componentsrequired for the reading apparatus Rb are accommodated in either thefirst hollow portion 10′ or the second hollow is portion 11′. The casing1′ is carried by a movable supporting member (not shown) in facingrelation to the white board WB′. The casing 1′ is caused to move in asecondary scanning direction N2′ by the non-illustrated supportingmember. While being moved in the direction N2′, the distance between thecasing 1′ and the white board WB′ is kept constant.

The lens array 2′ includes a plurality of convex lenses 20′ heldtogether by a holder 21′ made of e.g. a synthetic resin material. Thelens array 2′ is fitted into the first hollow portion 10′ and positionedat a predetermined height in the first hollow portion 10′. The convexlenses 20′ are arranged at regular intervals in a primary scanningdirection N1′ (FIG. 10) perpendicular to the secondary scanningdirection N2′ (FIG. 8). In the illustrated embodiment, the holder 21′ isprepared separately from the respective convex lenses 20′.Alternatively, the holder 21′ and the convex lenses 20′ may beintegrally made of a synthetic resin material. A linear image readingregion S′ on the white board WB′ extends in the primary scanningdirection N1′ and intersects the optical axes C′ of the respectiveconvex lenses 20′ (FIG. 8).

As shown in FIG. 8, the lens array cover 3′, which may be made of adark-colored (e.g. black) synthetic resin material, is fitted into thefirst hollow portion 10′ to come into direct contact with the upperportion of the lens array 2′. The lens array cover 3′ ensures properpositioning of the lens array 2′. The lens array cover 3′ is formed witha plurality of through-holes 30′ corresponding in number and position tothe convex lenses 20′, as seen from FIG. 10. Each through-hole 30′serves as a light-restricting aperture for adjusting the amount of lightincident on a relevant one of the convex lenses 20′. The center of eachthrough-hole 30′ coincides with the optical axis C′ of the relevantconvex lens 20′.

As shown in FIG. 8, the inner diameter d₁′ of each through-hole 30′ issmaller than the diameter d₂′ of the relevant convex lens 20′. In thismanner, light is prevented from entering each convex lens 20′ at itsradially outer portion (i.e., peripheral portion). Thus, the focusing oflight is performed only by the central portion of each convex lens 20′,which is advantageous for generating a clearly focused image through thelens 20′.

The light detectors 6′ are mounted on the obverse surface of thesubstrate 7′. As shown in FIG. 10, the light detectors 6′ are arrangedat regular intervals in the primary scanning direction N1′. As a result,the light receiving elements 60′ of the respective light detectors 6′are arranged in a row extending in the primary scanning direction N1′.The light receiving elements 60′ convert received light into an electricsignal based on the amount of the received light. The substrate 7′ isattached to the bottom portion of the casing 1′ to close the downwardopenings of the first and the second hollow portions 10′, 11′. As shownin FIGS. 8 and 10, each light detector 6′ is held in facing relation toa relevant one of the convex lenses 20′ when the substrate 7′ is fixedto the casing 1′. With such an arrangement, images illuminated at theimage reading region S′ are focused onto the light detectors 6′ throughthe convex lenses 20′, as shown in FIG. 10. According to the secondembodiment, the casing 1′ is provided with a plurality of partitions 19′to divide the first hollow portion 10′ into subdivisions. Eachsubdivision contains one convex lens 20′ and one light detector 6′. Thesubdivisions are separated from each other by the partitions 19′ so thatinterference of light is prevented.

Referring to FIG. 9, the light source 8′ includes a plurality of lightemitting devices 80′ such as: light-emitting diodes (LEDs). The lightemitting devices 80′, which are mounted on the obverse surface of thesubstrate 7′, are received in the second hollow portion 11′ when thesubstrate 7′ is attached to the casing 1′ (see also FIG. 8). As shown inFIG. 9, each light emitting device 80′ is offset from a correspondingone of the optical axes C′ in the primary scanning direction N1′.Preferably, as in the case of the image reading apparatus Ra of thefirst embodiment, each light emitting device 80′ may include acombination of two LEDs of different colors. One of these two LEDs maybe designed to emit green light, while the other may be designed to emitred light. With such an arrangement, when only the red LEDs are turnedon to emit red light, red portions of the images at the image readingregion S′ are not read out by the light detectors 8′. On the other hand,when the green LEDs are turned on, all the images at the image readingregion S′ may be read out by the light detectors 8′. Thus, by comparingthe read-out images obtained at one time (when only the red LEDs areturned on) with the other read-out images obtained at another time (whenonly the green LEDs are turned on), it is possible to distinguish thered portions from the other portions of the images at the image readingregion S′. In this manner, a two-color image-reading function can beperformed.

The first transparent member 4′ may be made of poly(methyl methacrylate)(PMMA) or polycarbonate (PC). As shown in FIG. 11, the first transparentmember 4′ is elongated in one direction and provided with a lightreceiving surface 40A′ and a light emitting surface 40B′. Both of thesesurfaces 40A′, 40B′ extend longitudinally of the first transparentmember 4′. The light receiving surface 40A′ is a smooth, downwardlyconvex surface, while the light emitting surface 40B′ is a smooth,upwardly convex surface. As shown in FIG. 8, the light receiving surface40A′ is wider than the light emitting devices 80′. The curvature of thelight emitting surface 40B′ is greater than that of the light receivingsurface 40A′.

As shown in FIGS. 8 and 11, the first transparent member 4′ is providedwith two leg portions 41′ each of which extends longitudinally of thefirst transparent member 4′. As best shown in FIG. 8, the leg portions41′ protrude downward beyond the light receiving surface 40A′. When thefirst transparent member 4′ is fitted into the second hollow portion 11′of the casing 1′, the two leg portions 41′ come into contact with theobverse surface of the substrate 7′. The light receiving surface 40A′ ofthe first transparent member 4′ is held in facing relation to the lightemitting devices 80′.

As shown in FIGS. 8 and 9, the second transparent member 5′ is elongatedin the primary scanning direction N1′ and has a generally plate-likeconfiguration. The second transparent member 5′ may be made of PMMA orPC. The second transparent member 5′ is provided with four smoothsurfaces: a first surface 50A′, a second surface 50B′, a third surface50C′ and a fourth surface 50D′. As shown in FIG. 8, the first surface50A′ serves as a light receiving surface, while the second surface 50B′serves as a light emitting surface. The third and the fourth surfaces50C′, 50D′ are designed to totally inwardly reflect light propagatingthrough the second transparent member 5′, so that the light is properlyled from the first surface 50A′ to the second surface 50B′.

Referring to FIGS. 8 and 12A, the second transparent member 5′ isprovided with a predetermined number of leg portions 51′ (51′a-51′d).The leg portions 51′ are disposed adjacent to the first surface awaitprotrude downward beyond the first surface 50A′. As shown in FIG. 12A,the leg portions 51′ are spaced from each other in the primary scanningdirection N1′. The first and the third leg portions 51′a, 51′c areprovided on the side of the third surface 50C′, while the second and thefourth leg portions 51′b, 51′d are provided on the side of the fourthsurface 50D′.

Differing from the illustrated arrangement, the first and the second legportions 51′a, 51′b may not be offset from each other in the primaryscanning direction N1′ but overlap. Likewise, the third and the fourthleg portions 5′c, 51′d may not be offset from each other in the primaryscanning direction N1′ but overlap.

Instead of the illustrated leg portions 51′, the second transparentmember 5′ may be provided with two leg portions each of which iselongated in the primary scanning direction N1′ like the leg portion 41′of the first transparent member 4′ (see FIG. 11).

As shown in FIG. 8, the lower portion of the second transparent member5′ is accommodated in the second hollow portion 11′ of the casing 1′,while the upper portion thereof protrudes from the casing 1 toward thewhite board WB′. The second transparent member 5′ is directly mounted onthe first transparent member 4′.

As shown in FIG. 8, the tips of the respective leg portions 51′ arefitted into positioning grooves 41 a′ (see also FIG. 11) formed in thefirst transparent member 4′. The intermediate portion of the secondtransparent member 5′ is held between two positioning edges 11 a′ of thecasing 1′. Further, as shown in FIGS. 12A and 12B, the longitudinalopposite ends of the second transparent member 5′ are formed withpositioning protrusions 52′. Accordingly, the casing 1′ is formed withgrooves into which the positioning protrusions 52′ are fitted (see FIG.9). With such an arrangement, the second transparent member 5′ is fixedto the casing 1′ with high positioning accuracy.

The first or light receiving surface 50A′ of the second transparentmember 5′ faces the light emitting surface 40A′ of the first transparentmember 4′ (see FIG. 8). The light receiving surface 50A′ is sinuous, asshown in FIG. 12A. Specifically, the light receiving surface 50A′ ismade up of a plurality of smoothly curved concaved portions 53′ and aplurality of smoothly curved convex portions 54′. The concaved portions53′ and the convex portions 54′ are disposed alternately with eachother. The concaved portions 53′ are arranged at a predetermined pitchP′ in the primary scanning direction N1′. The pitch P′ is equal to thepitch at which the convex lenses 20′ of the lens array 2′ are arranged.Thus, in FIG. 9 (i.e. as viewed in the secondary scanning direction),the apexes of the respective concaved portions 53′ coincide with theoptical axes C′ of the convex lenses 20′. Each light emitting device 80′is offset from a corresponding one of the optical axes C′ in the primaryscanning direction N1′ by a predetermined distance L′.

As shown in FIG. 8, the third surface 50C′ of the second transparentmember 5′ is not flat but bent. The fourth surface 50D′ is also bent tofollow the third surface 50C′. Consequently, the second surface 50B′ isproperly directed to the image reading region S.

The function of the image reading apparatus Rb will now be described.

Referring to FIG. 8, when the light emitting devices 80′ are turned on,the emitted light enters the first transparent member 4′ through thelight receiving surface 40A′. Then, the light propagates through thefirst transparent member 4′ and exits the transparent member 4′ via thelight emitting surface 40B′. Since the light receiving surface 40A′ andthe light emitting surface 40B′ are convex, the first transparent member4′ functions as a convex lens for the light. Thus, the first transparentmember 4′ causes the diverging light beams emitted from the light sourceto converge into generally parallel light beams.

It should be noted that the light receiving surface 40A′ of the firsttransparent member 4′ is much wider than the light emitting devices 80′.The advantage of this arrangement is as follows. Supposing that thedownward convex portion 49′ of the first transparent member 4′ has asmall width Lc, as shown in FIG. 13, and that the light emitting device80, is unduly offset from the optical axis Ca of the convex portion 49′,the diverging light beams emitted from the device 80′ may fail to becollected into parallel beams even if the deviation La is very small.However, the image reading apparatus Rb of the present invention doesnot encounter this problem since the light receiving surface 40A′ of thefirst transparent member 4′ has a large width. The large width of thelight receiving surface 40A′ is also advantageous in facilitating thereception of the light emitted from the light source.

Referring back to FIG. 8, after the light exits the first transparentmember 4′ via the light emitting surface 40B′, the light enters thesecond transparent member 5′ via the first surface 50A′. Then, the lightpropagates through the second transparent member 5′ from the firstsurface 50A′ toward the second surface 50B′. In this process, the lightmay strike the third surface 50C′ and/or the fourth surface 50D′.However, the third and the fourth surfaces 50C′, 50D′ can reflect thelight totally inwardly, thereby leading the light to the second surface50B′. As stated above, the light beams propagating through the secondtransparent member 5′ are parallel to each other. Thus, even when thewidth Lb of the second transparent member 5′ is small, the propagatinglight will be properly reflected inwardly.

The behavior of the propagating light viewed in the secondary scanningdirection N2′ is shown in FIG. 9. Originating from the light emittingdevices 80′, the light passes through the first transparent member 4′ asbeing slightly refracted. Then, the light strikes the first surface 50A′of the second transparent member 5′ at various positions at differentangles. As viewed in the primary scanning direction N1′, each lightemitting device 80′ is located between the apex of the adjacent convexportion 54′ and the adjacent optical axis C′. Thus, as illustrated, mostof the light emitted from the light emitting device 80′ will enter thesecond transparent member 5′ via the inclined portion of the firstsurface 50A′ which is located between the apex of the adjacent convexportion 54′ and the adjacent optical axis C′. Thus, most of the lightpropagating through the second transparent member 5′ is directed awayfrom the adjacent optical axis C′.

Consequently, as shown in FIG. 9, most of the light will converge atintermediate positions Ip between the optical axes C′ when it reachesthe second surface 50B′ of the second transparent member 5′. Though notillustrated in FIG. 9, the light beams emitted from the light emittingdevices 80′ also meet the portions of the first surface 50A′ which areadjacent to the optical axes C′. These light beams are refracted at thefirst surface 50A′ in a diverging manner to propagate through the secondtransparent member 5′ toward the second surface 50B′.

As understood from the above, the brightness at the second surface 50B′of the second transparent member 5′ is the lowest at positions Apadjacent to the optical axes C′, but the highest at the intermediatepositions Ip between the optical axes C′. The brightness graduallyincreases from the darkest positions Ap to the brightest positions Ip.Accordingly, the image reading region S′ is illuminated with generallythe same pattern of brightness. Thus, the image reading apparatus Rbincorporating the second transparent member 5′ enjoys the sameadvantages as the image reading apparatus Ra of the first embodiment.

As described above, the light receiving surface 40A′ and the lightemitting surface 40B′ of the first transparent member 4′ are bothcurved. Alternatively, either one of these surfaces may be flat.Further, preferably the convex light receiving surface 40A′ is muchwider than the light emitting devices, as described with reference toFIG. 8. According to the present invention, however, the light receivingsurface of the first transparent member may be formed with a partialconvex portion, as shown in FIG. 13.

FIG. 14 shows a modified light conducting unit U″ including a firsttransparent member 4″ and a second transparent member 5″. Theillustrated second transparent member 5″ is provided with a flat firstsurface 50A″ and a flat second surface 50B″. The first surface 50A″ ispartially shielded by light shielding members 55″ arranged between thefirst and the second transparent members 4″, 5″. In the illustratedexample, the light shielding members 55″ are attached to the secondtransparent member 5″. Alternatively, they may be attached to the firsttransparent member 4″.

The light shielding members 55″ are spaced from each other in theprimary scanning direction N1″. Each shielding member 55″ may be made ofa material having low transparency, so that the shielding member 55″ iscompletely opaque or semi-transparent (translucent). With such anarrangement, the same advantages can be enjoyed as in the case of thelight conducting unit U′ described above.

The present invention being thus described, it is obvious that the samemay be varied in many ways. For instance, a part of the first or secondtransparent member may be semi-transparent or opaque. A light shieldingmember may be attached to a surface other than the light receivingsurface and the light emitting surface of the first or secondtransparent member. Further, a third transparent member may be usedtogether with the first and the second transparent members to constitutea light conducting unit. Such variations are not to be regarded as adeparture from the spirit and scope of the present invention, and allsuch modifications as would be obvious to those skilled in the art areintended to be included within the scope of the following claims.

What is claimed is:
 1. An image reading apparatus comprising: a lightsource arranged to emit light for illuminating a linear image readingregion extending in a primary scanning direction; a plurality of lensesarranged in an array for focusing light reflected on the image readingregion and for producing reduced images, each of the lenses having anoptical axis which intersects a predetermined portion of the imagereading region; a plurality of light receiving elements for output ofimage signals based on the light focused by the lenses; and a lightconductor for leading the light emitted by the light source toward theimage reading region; wherein the light conductor leads the emittedlight so that said predetermined portion is illuminated more brightlythan other portions of the image reading region which are adjacent tosaid predetermined portion; and wherein the light conductor includes atransparent member having a first surface and a second surface, thefirst surface facing the light source, the second surface facing theimage reading region, the transparent member being arranged to leadlight from the first surface to the second surface so that distributionof light at the first surface is different from distribution of light atthe second surface.
 2. The apparatus according to claim 1, wherein thetransparent member is formed with a plurality of indents facing theimage reading region, each of the indents being provided with aninclined portion slanted relative to the first surface of thetransparent member.
 3. The apparatus according to claim 2, wherein thetransparent member is formed with a plurality of projections facing theimage reading region, each of the projections having a corner at which acutout is provided.
 4. The apparatus according to claim 2, wherein thelight source includes a plurality of light-emitting diodes arranged inan array, the light-emitting diodes being offset in the primary scanningdirection from the optical axes of the respective lenses.
 5. Theapparatus according to claim 4, wherein each of the light-emittingdiodes is held in facing relation to a relevant one of the inclinedportions of the indents.
 6. The apparatus according to claim 1, furthercomprising a casing for supporting the light source, the lenses, thelight receiving elements and the light conductor, the light conductorprotruding partially from the casing toward the image reading region. 7.The apparatus according to claim 1, wherein the first surface of thetransparent member is formed with a convex portion facing the lightsource.
 8. The apparatus according to claim 1, wherein the lightconductor includes a first transparent member and a second transparentmember.
 9. The apparatus according to claim 8, wherein the firsttransparent member is provided with a light receiving surface facing thelight source and a light emitting surface opposite to the lightreceiving surface, at least either one of the light receiving surfaceand the light emitting surface being provided with a convex portionextending in the primary scanning direction.
 10. The apparatus accordingto claim 9, wherein the second transparent member is formed separatelyfrom the first transparent member and arranged to lead light emittedfrom the light emitting surface toward the image reading region.
 11. Theapparatus according to claim 9, wherein both the light receiving surfaceand the light emitting surface of the first transparent member areconvex.
 12. The apparatus according to claim 9, wherein the secondtransparent member is provided with a light receiving surface held infacing relation to the light emitting surface of the first transparentmember.
 13. The apparatus according to claim 12, wherein the lightreceiving surface of the second transparent member is sinuous.
 14. Theapparatus according to claim 12, further comprising light shieldingmembers arranged between the light emitting surface of the firsttransparent member and the light receiving surface of the secondtransparent member.
 15. The apparatus according to claim 8, wherein thelight source includes a plurality of light-emitting diodes arranged inan array, the light-emitting diodes being offset in the primary scanningdirection from the optical axes of the respective lenses.
 16. Theapparatus according to claim 8, wherein the first and the secondtransparent members are fixed to each other.
 17. The apparatus accordingto claim 16, wherein the first transparent member is formed with apositioning groove, the second transparent member being formed with aleg portion fitted into the positioning groove of the first transparentmember.